CT Scan (CAT Scan): How Do They Work? - Medical News Today CT Scan (CAT Scan): How Do They Work? Written by Christian Nordqvist 3.5 33 A 'computerized tomography' (CT) (or 'computerized axial tomography' (CAT) scan) uses a computer that takes data from several X-ray images of structures inside a human's or animal's body and converts them into pictures on a monitor. Tomography is the process of generating a 2-dimensional image of a slice or section through a 3-dimensional object. Similar to looking at one slice of bread within the whole loaf. This article looks specifically at CT scans. We also have articles in our knowledge center about MRI scans , PET scans and ultrasound scans . Contents of this article: At the end of this article we include a list of recent developments on CT scans from MNT news. Fast facts on CT scans Here are some key points about CT scans. More detail and supporting information is in the main article. A CT scan uses data from several X-ray images of structures inside the body and converts them into pictures. The technique utilizes digital geometry processing to generate 3D images. CT scans are a source of ionizing radiation and can cause cancer .

A CT scanner emits a series of narrow beams through the human body, producing more detail than standard single beam X-rays. CT scanners are able to distinguish tissues inside a solid organ. Contrast dyes are sometimes used to improve the clarity of the image. CT scanning is particularly useful for getting detailed 3D images of certain parts of the body, such as soft tissues, blood vessels, and the brain. The images created are analyzed by radiologists. Unlike MRI scans, a CT scan uses X-rays. A CT scan is able to illustrate organ tear and organ injury quickly and so is often used for accident victims. What is a CT scan? A CT scanner uses digital geometry processing to generate a 3-dimensional (3D) image of the inside of an object. The 3D image is made after many 2-dimensional (2D) X-ray images are taken around a single axis of rotation - in other words, many pictures of the same area are taken from many angles and then placed together to produce a 3D image. The Greek word tomos means "slice", and the Greek word graphein means "write". Although CT is a useful tool for assisting diagnosis in medicine, it is a source of ionizing radiation and can cause cancer.

The National Cancer Institute 1 advises patients to discuss the risks and benefits of computerized tomography with their doctors. How do CT scans work? A CT imaging suite. A CT scanner emits a series of narrow beams through the human body as it moves through an arc, unlike an X-ray machine which sends just one radiation beam. The final picture is far more detailed than an X-ray image. Inside the CT scanner there is an X-ray detector which can see hundreds of different levels of density. It can see tissues inside a solid organ. This data is transmitted to a computer, which builds up a 3D cross-sectional picture of the part of the body and displays it on the screen. Sometimes a contrast dye is used because it shows up much more clearly on the screen. If a 3D image of the abdomen is required the patient may have to drink a barium meal. The barium appears white on the scan as it travels through the digestive system. If images lower down the body are required, such as the rectum, the patient may be given a barium enema. If blood vessel images are the target, the barium will be injected. The accuracy and speed of CT scans may be improved with the application of spiral CT.

The X-ray beam takes a spiral path during the scanning - it gathers continuous data with no gaps between images. For a spiral scan of the chest, for example, the patient will be asked to hold his/her breath for a few seconds. The video below, created by the UK's Open University, shows how a CT scan works. In this case the scan is being used to determine whether a patient has a fracture of the skull. What are CT scans like for patients? Most places will provide the patient with a gown. He/she will need to undress, usually down to their underwear, and put the gown on. If the place does not provide a gown the patient should wear loose-fitting clothes. Doctors may ask the patient to fast (eat nothing) and even refrain from consuming liquids for a specific period before the CT scan. The patient will be asked to lie down on a motorized examination table, which then goes into the giant doughnut-like CT scanner machine. The couch with the patient goes into the doughnut hole. Some patients may be given a contrast dye or substance which is either swallowed, given as an enema, or injected. This improves the picture of some blood vessels or tissues.

If a patient is allergic to contrast material he/she should tell the doctor beforehand. There are some medications that reduce allergic reactions to contrast materials. As metal interferes with the workings of the CT scanner the patient will need to remove all jewelry and metal fastenings. In the majority of cases the patient will lie on his/her back, facing up. But sometimes it may be necessary to lie face-down or sideways. After the machine has taken one X-ray picture, the couch will move slightly, and then another picture is taken, etc. The patient needs to lie very still for best results. During the scan everybody except for the patient will leave the room. The radiographer will still be able to communicate with the patient, and vice-versa, through an intercom. If the patient is a child, a parent or adult might be allowed to stand or sit nearby - that person will have to wear a lead apron to prevent radiation exposure. CT scans and pregnancy - any woman who suspects she may be pregnant should tell her doctor beforehand. The UK's National Health Service 2 warns that CT scans are not recommended for pregnant mothers because of the risk that X-rays might harm the unborn baby.

CT scans and claustrophobia - patients who suffer from claustrophobia need to tell their doctor or radiographer beforehand, advises Cancer Research UK 3. The patient may be given an injection or tablet to calm them down before the scan. CT scans and breastfeeding - the State Government of Victoria 4 in Australia says that mothers should avoid breastfeeding their babies for about 24 hours after a CT scan if an iodinated intravenous dye was used. The dye may pass into the breast milk. If you are breastfeeding, tell your doctor beforehand. On the next page we look at when CT scans are used, who analyzes the image and the difference between CT scans and MRI scans. CT scan - Mayo Clinic CT scan CT scan slices A computerized tomography (CT) scan combines a series of X-ray images taken from different angles and uses computer processing to create cross-sectional images, or slices, of the bones, blood vessels and soft tissues inside your body. CT scan images provide more detailed information than plain X-rays do. A CT scan has many uses, but is particularly well-suited to quickly examine people who may have internal injuries from car accidents or other types of trauma.

A CT scan can be used to visualize nearly all parts of the body and is used to diagnose disease or injury as well as to plan medical, surgical or radiation treatment. Radiation-emitting products: Computed tomography (CT). U.S. Food and Drug Administration. Accessed Dec. 23, 2014. Computed tomography (CT) — Body. Radiological Society of North America. Accessed Dec. 23, 2014. Contrast materials. RadiologyInfo.org. Accessed Dec. 29, 2014. Products and Services Body CT (CAT Scan) What are the limitations of CT Scanning of the Body? What is CT Scanning of the Body? Computed tomography, more commonly known as a CT or CAT scan, is a diagnostic medical test that, like traditional x-rays, produces multiple images or pictures of the inside of the body. The cross-sectional images generated during a CT scan can be reformatted in multiple planes, and can even generate three-dimensional images. These images can be viewed on a computer monitor, printed on film or transferred to a CD or DVD.

CT images of internal organs, bones, soft tissue and blood vessels typically provide greater detail than traditional x-rays, particularly of soft tissues and blood vessels. Using specialized equipment and expertise to create and interpret CT scans of the body, radiologists can more easily diagnose problems such as cancer, cardiovascular disease, infectious disease, appendicitis, trauma and musculoskeletal disorders. What are some common uses of the procedure? CT imaging is: one of the fastest and most accurate tools for examining the chest, abdomen and pelvis because it provides detailed, cross-sectional views of all types of tissue. used to examine patients with injuries from trauma such as a motor vehicle accident. performed on patients with acute symptoms such as chest or abdominal pain or difficulty breathing. often the best method for detecting many different cancers, such as lymphoma and cancers of the lung, liver, kidney, ovary and pancreas since the image allows a physician to confirm the presence of a tumor, measure its size, identify its precise location and determine the extent of its involvement with other nearby tissue. an examination that plays a significant role in the detection, diagnosis and treatment of vascular diseases that can lead to stroke, kidney failure or even death.

CT is commonly used to assess for pulmonary embolism (a blood clot in the lung vessels) as well as for aortic aneurysms. invaluable in diagnosing and treating spinal problems and injuries to the hands, feet and other skeletal structures because it can clearly show even very small bones as well as surrounding tissues such as muscle and blood vessels. In pediatric patients, CT imaging is often used to evaluate: lymphoma severe injuries Radiologists and radiation oncologists often use the CT examination to: quickly identify injuries to the lungs, heart and vessels, liver, spleen, kidneys, bowel or other internal organs in cases of trauma. guide biopsies and other procedures such as abscess drainages and minimally invasive tumor treatments. plan for and assess the results of surgery, such as organ transplants or gastric bypass. stage, plan and properly administer radiation treatments for tumors as well as monitor response to chemotherapy. measure bone mineral density for the detection of osteoporosis. top of page How should I prepare? You should wear comfortable, loose-fitting clothing to your exam. You may be given a gown to wear during the procedure.

Metal objects, including jewelry, eyeglasses, dentures and hairpins, may affect the CT images and should be left at home or removed prior to your exam. You may also be asked to remove hearing aids and removable dental work. Women will be asked to remove bras containing metal underwire. You may be asked to remove any piercings, if possible. You will be asked not to eat or drink anything for a few hours beforehand, as contrast material will be used in your exam. You should inform your physician of all medications you are taking and if you have any allergies. If you have a known allergy to contrast material, or "dye," your doctor may prescribe medications (usually a steroid) to reduce the risk of an allergic reaction. These medications generally need to be taken 12 hours prior to administration of contrast material. To avoid unnecessary delays, contact your doctor before the exact time of your exam. Also inform your doctor of any recent illnesses or other medical conditions and whether you have a history of heart disease, asthma, diabetes, kidney disease or thyroid problems. Any of these conditions may increase the risk of an unusual adverse effect. Women should always inform their physician and the CT technologist if there is any possibility that they may be pregnant.

See the Safety page for more information about pregnancy and x-rays. top of page What does the equipment look like? The CT scanner is typically a large, box-like machine with a hole, or short tunnel, in the center. You will lie on a narrow examination table that slides into and out of this tunnel. Rotating around you, the x-ray tube and electronic x-ray detectors are located opposite each other in a ring, called a gantry. The computer workstation that processes the imaging information is located in a separate control room, where the technologist operates the scanner and monitors your examination in direct visual contact and usually with the ability to hear and talk to you with the use of a speaker and microphone. top of page How does the procedure work? In many ways CT scanning works very much like other x-ray examinations. Different body parts absorb the x-rays in varying degrees. It is this crucial difference in absorption that allows the body parts to be distinguished from one another on an x-ray film or CT electronic image. In a conventional x-ray exam, a small amount of radiation is aimed at and passes through the part of the body being examined, recording an image on a special electronic image recording plate.

Bones appear white on the x-ray; soft tissue, such as organs like the heart or liver, shows up in shades of gray, and air appears black. With CT scanning, numerous x-ray beams and a set of electronic x-ray detectors rotate around you, measuring the amount of radiation being absorbed throughout your body. Sometimes, the examination table will move during the scan, so that the x-ray beam follows a spiral path. A special computer program processes this large volume of data to create two-dimensional cross-sectional images of your body, which are then displayed on a monitor. CT imaging is sometimes compared to looking into a loaf of bread by cutting the loaf into thin slices. When the image slices are reassembled by computer software, the result is a very detailed multidimensional view of the body's interior. Refinements in detector technology allow nearly all CT scanners to obtain multiple slices in a single rotation. These scanners, called multislice CT or multidetector CT, allow thinner slices to be obtained in a shorter period of time, resulting in more detail and additional view capabilities. Modern CT scanners are so fast that they can scan through large sections of the body in just a few seconds, and even faster in small children.

Such speed is beneficial for all patients but especially children, the elderly and critically ill, all of whom may have difficulty in remaining still, even for the brief time necessary to obtain images. For children, the CT scanner technique will be adjusted to their size and the area of interest to reduce the radiation dose. For some CT exams, a contrast material is used to enhance visibility in the area of the body being studied. top of page How is the CAT scan performed? The technologist begins by positioning you on the CT examination table, usually lying flat on your back. Straps and pillows may be used to help you maintain the correct position and to help you remain still during the exam. Many scanners are fast enough that children can be scanned without sedation. In special cases, sedation may be needed for children who cannot hold still. Motion will cause blurring of the images and degrade the quality of the examination the same way that it affects photographs. If contrast material is used, depending on the type of exam, it will be swallowed, injected through an intravenous line (IV) or, rarely, administered by enema. Next, the table will move quickly through the scanner to determine the correct starting position for the scans.

Then, the table will move slowly through the machine as the actual CT scanning is performed. Depending on the type of CT scan, the machine may make several passes. You may be asked to hold your breath during the scanning. Any motion, whether breathing or body movements, can lead to artifacts on the images. This loss of image quality can resemble the blurring seen on a photograph taken of a moving object. When the examination is completed, you will be asked to wait until the technologist verifies that the images are of high enough quality for accurate interpretation. The CT examination is usually completed within 30 minutes. The portion requiring intravenous contrast injection usually lasts only 10 to 30 seconds. top of page What will I experience during and after the procedure? CT exams are generally painless, fast and easy. With multidetector CT, the amount of time that the patient needs to lie still is reduced. Though the scanning itself causes no pain, there may be some discomfort from having to remain still for several minutes and with placement of an IV. If you have a hard time staying still, are very nervous or anxious or have chronic pain, you may find a CT exam to be stressful.

The technologist or nurse, under the direction of a physician, may offer you some medication to help you tolerate the CT scanning procedure. For exams (excluding head and neck) your head will remain outside the hole in the center of the scanner. The scanner is approximately 24 inches wide, therefore, your entire body will be "inside" the scanner at one time such as with MRI. If an intravenous contrast material is used, you will feel a pin prick when the needle is inserted into your vein. You will likely have a warm, flushed sensation during the injection of the contrast materials and a metallic taste in your mouth that lasts for at most a minute or two. You may experience a sensation like you have to urinate; however, this is actually a contrast effect and subsides quickly. If the contrast material is swallowed, you may find the taste mildly unpleasant; however, most patients can easily tolerate it. You can expect to experience a sense of abdominal fullness and an increasing need to expel the liquid if your contrast material is given by enema. In this case, be patient, as the mild discomfort will not last long.

When you enter the CT scanner room, special light lines may be seen projected onto your body, and are used to ensure that you are properly positioned. With modern CT scanners, you will hear only slight buzzing, clicking and whirring sounds as the CT scanner's internal parts, not usually visible to you, revolve around you during the imaging process. You will be alone in the exam room during the CT scan, unless there are special circumstances. For example, sometimes a parent wearing a lead shield may stay in the room with their child. However, the technologist will always be able to see, hear and speak with you through a built-in intercom system. With pediatric patients, a parent may be allowed in the room but will be required to wear a lead apron to minimize radiation exposure. After a CT exam, the intravenous line used to inject the contrast material will be removed by the technologist, and the tiny hole made by the needle will be covered with a small dressing. You can return to your normal activities. top of page Who interprets the results and how do I get them?

A radiologist with expertise in supervising and interpreting radiology examinations will analyze the images and send an official report to your primary care physician or physician who referred you for the exam, who will discuss the results with you. Follow-up examinations may be necessary, and your doctor will explain the exact reason why another exam is requested. Sometimes a follow-up exam is done because a potential abnormality needs further evaluation with additional views or a special imaging technique. A follow-up examination may also be necessary so that any change in a known abnormality can be monitored over time. Follow-up examinations are sometimes the best way to see if treatment is working or if a finding is stable or changed over time. What are the benefits vs. risks? Benefits CT scanning is painless, noninvasive and accurate. A major advantage of CT is its ability to image bone, soft tissue and blood vessels all at the same time. Unlike conventional x-rays, CT scanning provides very detailed images of many types of tissue as well as the lungs, bones, and blood vessels. CT examinations are fast and simple; in emergency cases, they can reveal internal injuries and bleeding quickly enough to help save lives. CT has been shown to be a cost-effective imaging tool for a wide range of clinical problems.

CT is less sensitive to patient movement than MRI. CT can be performed if you have an implanted medical device of any kind, unlike MRI. CT imaging provides real-time imaging, making it a good tool for guiding minimally invasive procedures such as needle biopsies and needle aspirations of many areas of the body, particularly the lungs, abdomen, pelvis and bones. A diagnosis determined by CT scanning may eliminate the need for exploratory surgery and surgical biopsy. No radiation remains in a patient's body after a CT examination. X-rays used in CT scans should have no immediate side effects. Risks There is no conclusive evidence that radiation at small amounts delivered by a CT scan causes cancer. Large population studies have shown a slight increase in cancer from much larger amounts of radiation, such as from radiation therapy. Thus, there is always concern that this risk may also apply to the lower amounts of radiation delivered by a CT exam. When a CT scan is recommended by your doctor, the expected benefit of this test outweighs the potential risk from radiation. You are encouraged to discuss the risks versus the benefits of your CT scan with your doctor or radiologist, and to explore whether alternative imaging tests may be available to diagnose your condition. The effective radiation dose for this procedure varies.

See the Safety page for more information about radiation dose. Women should always inform their physician and x-ray or CT technologist if there is any possibility that they are pregnant. See the Safety page for more information about pregnancy and x-rays. CT scanning is, in general, not recommended for pregnant women unless medically necessary because of potential risk to the baby in the womb. Manufacturers of intravenous contrast indicate mothers should not breastfeed their babies for 24-48 hours after contrast medium is given. However, both the American College of Radiology (ACR) and the European Society of Urogenital Radiology note that the available data suggest that it is safe to continue breastfeeding after receiving intravenous contrast. For further information please consult the ACR Manual on Contrast Media and its references. The risk of serious allergic reaction to contrast materials that contain iodine is extremely rare, and radiology departments are well-equipped to deal with them. Because children are more sensitive to radiation, they should have a CT exam only if it is essential for making a diagnosis and should not have repeated CT exams unless absolutely necessary. CT scans in children should always be done with low-dose technique. top of page What are the limitations of CT Scanning of the Body?

Soft-tissue details in areas such as the brain, internal pelvic organs, and joints (such as knees and shoulders) can often be better evaluated with magnetic resonance imaging (MRI). In pregnant women, while CT can be performed safely, other imaging exams not involving radiation, such as ultrasound or MRI, are preferred but only if they are likely to be as good as CT in diagnosing your condition. A person who is very large may not fit into the opening of a conventional CT scanner or may be over the weight limit—usually 450 pounds—for the moving table. CT Scan (Computerized Tomography): Read About the Procedure Medical Author: Melissa Conrad Stöppler, MD Melissa Conrad Stöppler, MD Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

Medical Editor: Charles Patrick Davis, MD, PhD Charles Patrick Davis, MD, PhD Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications. Share Your Story Computerized (or computed) tomography, and often formerly referred to as computerized axial tomography (CAT) scan, is an X-ray procedure that combines many X-ray images with the aid of a computer to generate cross-sectional views and, if needed, three-dimensional images of the internal organs and structures of the body. Computerized tomography is more commonly known by its abbreviated names, CT scan or CAT scan. A CT scan is used to define normal and abnormal structures in the body and/or assist in procedures by helping to accurately guide the placement of instruments or treatments.

A large donut-shaped X-ray machine or scanner takes X-ray images at many different angles around the body. These images are processed by a computer to produce cross-sectional pictures of the body. In each of these pictures the body is seen as an X-ray "slice" of the body, which is recorded on a film. This recorded image is called a tomogram. "Computerized axial tomography" refers to the recorded tomogram "sections" at different levels of the body. Imagine the body as a loaf of bread and you are looking at one end of the loaf. As you remove each slice of bread, you can see the entire surface of that slice from the crust to the center. The body is seen on CT scan slices in a similar fashion from the skin to the central part of the body being examined. When these levels are further "added" together, a three-dimensional picture of an organ or abnormal body structure can be obtained. Medically Reviewed by a Doctor on 11/6/2015 CT Scan Glossary of Terms with Medical Definitions See the entire definition of Arthritis Asthma: A common lung disorder in which inflammation causes the bronchi to swell and narro...

See the entire definition of Asthma Autopsy: A postmortem examination. Also known as necropsy. Barium: 1. A metallic element belonging to the alkaline earths with an atomic numbe... See the entire definition of Barium Bowel: The small and large intestine. Brain: The portion of the central nervous system that is located within the skull. It func... See the entire definition of Brain Breathing: The process of respiration, during which air is inhaled into the lungs through ... See the entire definition of Breathing Cancer: An abnormal growth of cells which tend to proliferate in an uncontrolled way and, ... See the entire definition of Cancer CAT scan: Computerized axial tomography scan. CAT scanning is a painless X-ray test in whi... See the entire definition of Diagnosis Disc: Shortened terminology for an intervertebral disc, a disk-shaped piece of specialized... See the entire definition of Disc Dizziness: Painless head discomfort with many possible causes including disturbances of ... See the entire definition of Dizziness Ear: The hearing organ. There are three sections of the ear, according to the anatomy tex...

See the entire definition of Ear Emphysema: is a lung condition featuring an abnormal accumulation of air due to enlargemen... See the entire definition of Emphysema Flush: (1) A redness of the skin, typically over the cheeks or neck. A flush is usually ... See the entire definition of Flush Fracture: A break in bone or cartilage. Although usually a result of trauma, a fracture ca... See the entire definition of Fracture Gastrointestinal: Adjective referring collectively to the stomach and small and large inte... See the entire definition of Gastrointestinal Gastrointestinal tract: The stomach and intestines. Abbreviated GI tract....See the entire definition of Gastrointestinal tract Godfrey Hounsfield: See: Hounsfield, Godfrey. Heart: The muscle that pumps blood received from veins into arteries throughout the body. ... See the entire definition of Heart Heart disease: Any disorder that affects the heart. Sometimes the term "heart disease" is ... See the entire definition of Hounsfield Itching: An uncomfortable sensation in the skin that feels as if something is crawling on ...

See the entire definition of Itching Kidney: One of a pair of organs located in the right and left side of the abdomen. The kid... See the entire definition of Kidney Large bowel: Another name for the large intestine. Leg: In popular usage, the part of the body from the top of the thigh down to the foot, an... See the entire definition of Leg Liver: The largest solid organ in the body, situated in the upper part of the abdomen on t... See the entire definition of Liver Lymph: The almost colorless fluid that travels through the lymphatic system, carrying cell... See the entire definition of Lymph Middle ear: A part of the ear that consists of the eardrum (tympanic membrane) and, beyond... See the entire definition of Neck Obstruction: Blockage of a passageway. See, for example: Airway obstruction; Intestinal o... See the entire definition of Obstruction Outpatient: A patient who is not hospitalized, but instead comes to a physician?s office, ... See the entire definition of Outpatient Pain: An unpleasant sensation that can range from mild, localized discomfort to agony. Pa...

See the entire definition of Pain Pancreas: A spongy, tube-shaped organ that is about 6 inches long and is located in the ba... See the entire definition of Pancreas Pelvic: Having to do with the pelvis, the lower part of the abdomen, located between the h... See the entire definition of Pelvic Pelvis: The lower part of the abdomen, located between the hip bones. Structures in the fe... See the entire definition of Pelvis Pneumonia: Inflammation of one or both lungs, with dense areas of lung inflammation. Pneum... See the entire definition of Pneumonia Radiation: 1. Rays of energy. Gamma rays and X-rays are two of the types of energy ... See the entire definition of Radiation Radiograph: In medicine, an X-ray or a film produced through X-ray.... See the entire definition of Radiograph Radiologist: A physician specialized in radiology, the branch of medicine that uses ionizi... See the entire definition of Radiologist Scan: As a noun, the data or image obtained from the examination of organs or regions of... See the entire definition of Scan Sinus: 1.

An air-filled cavity in a dense portion of a skull bone. The sinuses decr... See the entire definition of Sinus Skull: The skull is a collection of bones which encase the brain and give form to the hea... See the entire definition of Skull Spinal stenosis: Narrowing of the spinal canal. Spinal stenosis is most commonly caused by... See the entire definition of Spine Spleen: An organ that is located in the upper-left part of the abdomen, not far from the s... See the entire definition of Spleen Stenosis: A narrowing. For example, aortic stenosis is a narrowing of the aortic valve in ... See the entire definition of Stenosis Stomach: The digestive organ that is located in the upper abdomen, under the ribs. The upp... See the entire definition of Stomach Stroke: The sudden death of brain cells due to lack of oxygen, caused by blockage of blood... See the entire definition of Stroke Surgery: The branch of medicine that employs operations in the treatment of disease or inj... See the entire definition of Surgery Tomography: The process for generating a tomogram, a two-dimensional image of a slice or s...

See the entire definition of Tomography Ultrasound: High-frequency sound waves. Ultra-sound waves can be bounced off tissues by us... See the entire definition of Ultrasound Vein: A blood vessel that carries blood that is low in oxygen content from the body back t... See the entire definition of Vein Vessel: A tube in the body that carries fluids. Examples of vessels are blood vessels and ... See the entire definition of Vessel X-ray: High-energy radiation with waves shorter than those of visible light. X-ray is used... Medical CT Medical CT What is a CAT scanner and what does CAT stand for? "CAT" stands for "computed axial tomography" and often the "axial" is dropped, leaving CT to define this particular imaging modality. This technique produces a series of images at various depths in the body (slices). This is in contrast to conventional x rays in which all the structures of the body throughout the depth are superimposed on each other in a single film. To make the image, the patient is placed in a donut-shaped gantry. An x-ray tube is rotated around the patient and the patient is exposed to a narrow beam of x rays. A ring of detectors measures the radiation transmitted through the patient.

(Radiation is transmitted differently through different structures, such as the various organs and bones, in the body.) This transmitted data is then used to construct images of body "slices." CT is better for imaging certain structures since, as mentioned, it eliminates the superimposition of organs and bones in the body. For example, if a patient has lung nodules, you can see them in a plain film (like a chest x ray), but you can't tell how deep they are or what their exact structure is. By looking at a CT "slice" of the lung and processing the data to enhance the nodules, their location and size can better be defines. Many of your answers state that the effective dose of an abdominal CT scan is 10 mSv. However, yesterday morning I spoke with the radiation safety officer at a local university who claims that the range for the same procedure with contrast is only 1-3 mSv and that the abdominal-pelvic CT, again with contrast, is only 4-6 mSv. Can you explain the discrepancy?

Doses received by patients for any diagnostic exam will vary depending on the type of equipment, settings of equipment (for example, kVp, mAs, etc.) number of pictures, with or without contrast, patient size, and some other miscellaneous items. According to Wall and Hart (1997), abdominal or pelvic CT results in an effective dose of about 10 mSv and can vary from 3 to 14 mSv. The numbers used on the Health Physics Society Ask the Experts section of the website are those printed in the literature and not based on a single organization. Reference Wall BF, Hart D. Revised radiation doses for typical x-ray examinations. Report on a recent review of doses to patients from medical x-ray examinations in the UK by NRPB. National Radiological Protection Board. British Journal of Radiology 70(833): 437-9; May 1997. I recently had a cervical CT scan done. I have been feeling sick since then. I am concerned about the dose of radiation I received so have tried calling around here locally but have no idea how to investigate this or resolve this.

The facility where the CT was taken indicates that patients do not get exposed to very much radiation during a CT scan. What can I do to determine my dose? If you want actual radiation dose numbers from the facility where the CT scan was performed, you can request a dose estimate from the facility's radiologist or medical physicist. Even if the facility does not have a radiologist or medical physicist on-site, it must have qualified staff available to read the x-ray films and calibrate the x-ray equipment. There is nothing in the literature, however, to suggest that the amount of radiation from a standard diagnostic CT scan would cause an increase in your body temperature or make you feel sick. Radiation doses to patients from standard diagnostic exams are well below the doses necessary to cause biological effects. Is there a way to find out how many CT scan slices were used after the scan is done? Is the dose information stored in a computer? Information about x-ray procedures is recorded on an x-ray request form and included in the radiologist's dictation of the study results. This would include the number of slices and the scanning parameters (from which dose can be calculated). The information posted on this web page is intended as general reference information only.

Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society. © 2016 Health Physics Society Computed Tomography Angiography (CTA) | Johns Hopkins Medicine Health Library Computed Tomography Angiography (CTA) (CTA) What is a CTA? CT angiography is a type of medical exam that combines a CT scan with an injection of a contrast media to produce pictures of blood vessels and tissues in a part of your body. The contrast is injected through an intravenous (IV) line started in your arm or hand. A computerized tomography scan, or CT scan, is a type of X-ray that uses a computer to make cross-sectional images of your body.

The media injected to perform CT angiography is called a contrast material because it "lights up" blood vessels and tissues that are being studied. What are the reasons for a CTA? You may need this medical test if you have an abnormality that involves the blood vessels of your brain, heart, lungs, kidneys, or other parts of your body. Doctors may use the information from this test to learn more about your condition and to decide the best way to treat you. Some reasons to have a CT angiogram include: To find an aneurysm (a blood vessel that has become enlarged and may be in danger of rupturing) To find blood vessels that have become narrowed by atherosclerosis (fatty material that forms plaques in the walls of arteries) To find abnormal blood vessel formations inside your brain To identify blood vessels damaged by injury To find blood clots that may have formed in your leg veins and traveled into your lungs. To evaluate a tumor that is fed by blood vessels Information from CT angiography may help prevent a stroke or a heart attack . This type of test may also help your doctor plan cancer treatment or prepare you for a kidney transplant . Your doctor may have other reasons for ordering this test.

Make a Health Promise Heart disease remains the number one killer nationwide. To help prevent heart disease or catch symptoms early, adults over 50 should have a full cardiovascular assessment. A coronary calcium scan can show just how at risk you are for a heart attack or other heart issues before other signs and symptoms occur. This is particularly useful for those with a family history of heart disease or other significant risk factors. Share your health promise on Twitter and Facebook: What are the risks of a CTA? There is always a slight risk for cancer from repeated exposure to radiation, but the benefits of getting an accurate diagnosis generally outweigh the risks. The amount of radiation used during CT angiography is considered minimal, so the risk for radiation exposure is low. No radiation remains in your body after a CT scan. Other risks include: Allergic reactions. Always let your radiologist know if you have any history of allergies or an allergy to contrast material. Reactions to contrast are uncommon. If you have any history of allergic reactions, you may be given medication to lessen the risk for an allergic reaction before the test. Tissue damage. If a large amount of contrast material leaks around your IV site, it can irritate your skin or the blood vessels and nerves just under your skin.

It is important to tell your radiologist or radiology technician if you have any pain when the contrast material is injected through your IV. Angiography contrast material can damage your kidneys, so you may not be able to have this test if you have severe kidney disease or diabetes . If you are breastfeeding, you may want to wait for 12 to 24 hours after this test before nursing your baby. If you are pregnant or suspect that you may be pregnant, you should notify your doctor or radiology technician. There may be other risks, depending on your specific medical condition. Be sure to discuss any concerns with your doctor or radiology technician before the procedure. How do I prepare for a CTA? PRECAUTIONS: If you are pregnant or think you may be pregnant, please check with your doctor before scheduling the exam. Other options will be discussed with you and your doctor. CLOTHING: You may be asked to change into a patient gown. If so, a gown will be provided for you. A lock will be provided to secure all personal belongings. Please remove all piercings and leave all jewelry and valuables at home. CONTRAST MEDIA: CT scans are most frequently done with and without a contrast media.

The contrast media improves the radiologist's ability to find structures that are abnormal. Some patients should not have an iodine-based contrast media. If you have problems with your kidney function, please inform us in advance. We may be able to perform the scan without the contrast media or may be able to find an alternate imaging exam. You will be asked to sign a consent form that will detail the risks and side-effects associated with contrast media injected through an intravenous (IV) line (small tube placed in a vein). ALLERGY: Please inform the access center representative when you schedule your scan if you have had an allergic reaction to any contrast media. IV contrast will not be administered if you have had a severe or anaphylactic reaction to any contrast media in the past. Mild to moderate reactions warrant a plan that includes taking medication prior to the CT examination. These plans will be discussed with you in detail when you schedule your exam. Any known reactions to a contrast media should be discussed with your personal physician. EAT/DRINK: If your study was ordered without contrast, you can eat, drink and take your prescribed medications prior to your exam. If your doctor orders a CT scan with contrast, do not eat anything three hours before your CT scan.

You are encouraged to drink clear liquids. You may also take your prescribed medications prior to your exam. If you are undergoing a chest CTA, do not consume any caffeine or exercise three hours prior to your appointment. DIABETICS: Diabetics should eat a light breakfast or lunch three hours prior to the scan time. Depending on your oral medication for diabetes, you may be asked to discontinue use of the medication for 48 hours after the CT examination. Detailed instructions will be given following your examination. MEDICATION: All patients can take their prescribed medications as usual. Based on your medical condition, your doctor may request other specific preparation. What happens during a CTA? You may have this exam done at the hospital or at another outpatient facility. The CT scanner is a large machine with a tunnel that the examining table passes in and out of. Procedures may vary depending on your condition and your doctor's practices. You may be asked to change into a patient gown If so, a gown will be provided for you. A locker will be provided to secure all personal belongings. Please remove all piercings and leave all jewelry and valuables at home. You will lie on a scan table that slides into a large, circular opening of the scanning machine.

Pillows and straps may be used to prevent movement during the procedure. The technologist will be in another room where the scanner controls are located. However, you will be in constant sight of the technologist through a window. Speakers inside the scanner will enable the technologist to communicate with and hear you. You may have a call button so that you can let the technologist know if you have any problems during the procedure. The technologist will be watching you at all times and will be in constant communication. As the scanner begins to rotate around you, X-rays will pass through the body for short amounts of time. You will hear clicking sounds, which are normal. The X-rays absorbed by the body's tissues will be detected by the scanner and transmitted to the computer. The computer will transform the information into an image to be interpreted by the radiologist. It will be important that you remain very still during the procedure. You may be asked to hold your breath at various times during the procedure. If contrast media is used for your procedure, you may feel some effects when the contrast is injected into the IV line. These effects include a flushing sensation, a salty or metallic taste in the mouth, a brief headache, or nausea and/or vomiting.

These effects usually last for a few moments. You should notify the technologist if you feel any breathing difficulties, sweating, numbness or heart palpitations. When the procedure is complete, you will be removed from the scanner. If an IV line was inserted for contrast media, the line will be removed. While the CTA exam itself causes no pain, having to lie still for the length of the procedure mgiht cause some discomfort or pain, particularly in the case of a recent injury or invasive procedure such as surgery. The technologist will use all possible comfort measures and complete the procedure as quickly as possible to minimize any discomfort or pain. What happens after a CTA? If contrast media was used during your procedure, you may be monitored for a period of time for any side effects or reactions to the contrast, such as itching, swelling, rash or difficulty breathing. If you notice any pain, redness, and/or swelling at the IV site after you return home following your CTA scan, you should notify your doctor as this could indicate an infection or other type of reaction. Otherwise, there is no special type of care required after a CTA scan. You may resume your usual diet and activities unless your doctor advises you differently.

Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation. Experience Our Care PET scan: MedlinePlus Medical Encyclopedia URL of this page: //medlineplus.gov/ency/article/003827.htm PET scan A positron emission tomography scan is a type of imaging test. It uses a radioactive substance called a tracer to look for disease in the body. A positron emission tomography (PET) scan shows how organs and tissues are working. This is different than MRI and CT scans. These tests show the structure of, and blood flow to and from organs. Machines that combine the PET and CT images, called a PET/CT, are commonly used. How the Test is Performed A PET scan uses a small amount of radioactive tracer. The tracer is given through a vein (IV). The needle is most often inserted on the inside of your elbow. The tracer travels through your blood and collects in organs and tissues. This helps the radiologist see certain areas more clearly. You will need to wait as the tracer is absorbed by your body. This takes about 1 hour. Then, you will lie on a narrow table that slides into a large tunnel-shaped scanner. The PET detects signals from the tracer.

A computer changes the signals into 3D pictures. The images are displayed on a monitor for your health care provider to read. You must lie still during the test. Too much movement can blur images and cause errors. How long the test takes depends on what part of the body is being scanned. How to Prepare for the Test You may be asked not to eat anything for 4 to 6 hours before the scan. You will be able to drink water but not other beverages including coffee. If you have diabetes, your provider will tell you not to take your diabetes medicine before the test. These medicines will interfere with the results. Tell your provider if: You are afraid of close spaces (have claustrophobia). You may be given a medicine to help you feel sleepy and less anxious. You are pregnant or think you might be pregnant. You have any allergies to injected dye (contrast). Always tell your provider about the medicines you are taking. Let your provider know about the medicines you bought without a prescription. Sometimes, medicines may interfere with the test results. How the Test will Feel You may feel a sharp sting when the needle with the tracer is placed into your vein. A PET scan causes no pain.

The table may be hard or cold, but you can request a blanket or pillow. An intercom in the room allows you to speak to someone at any time. There is no recovery time, unless you were given a medicine to relax. Why the Test is Performed A PET scan can reveal the size, shape, position, and some function of organs. The most common use for a PET scan is for cancer, when it may be done: To see how far cancer has spread. This helps to select the best treatment approach. To check how well your cancer is responding, either during treatment or after treatment is completed. This test can also be used to: Check brain function

Question: In the medical procedure CT scan, for what does the letter T stand?
Answer: (COMPUTERISED) TOMOGRAPHY